Pulse tube refrigeration with a fluid switching means



April 13, 1967 F. H. GREEN I 3,314,244

PULSE TUBE REFRIGERATION WITH A FLUID SWITCHING MEANS Filed April 26,1966 1'6: 5 fizf ae/a /7. 6266/1/ INVENTOR.

United States Patent 0 3,314,244 PULSE TUBE REFRIGERATION WITH A FLUIDSWITCHING MEANS Frederick H. Green, Palos Verdes Estates, Calif.,assignor to The Garrett Corporation, Los Angeles, Calif a corporation ofCalifornia Filed Apr. 26, 1966, Ser. No. 545,444 11 Claims. (Cl. 62-88)This invention relates to an improved laminar flow cooling device inwhich very low temperature refrigeration is achieved by means of anoscillating pressure exerted in a gas filled tubular enclosure and, moreparticularly, to a means for oscillating the pressure which meanscontains no moving parts.

In a United States Patent No. 3,237,421 there is disclosed a Pulse TubeRefrigerator wherein the pressure of the gas in a tubular enclosure isoscillated and the flow of gas within the enclosure is restricted tolaminar flow, i.e., parallel to the axis of the enclosure. At one end ofthe enclosure there is a heat exchanger that removes heat from thecompressed gas. Then, after a few pressure oscillations, a significanttemperature gradient is induced along the axis within the tubularenclosure. The pulse tube refrigerator requires no moving parts in therefrigeration section but only requires means to oscillate the pressuretherein. In the prior art, two mechanical valves are provided to controlthe oscillation of gas pressure within the enclosure. The valves areactuated by an operator whenever his judgment determines that the firstvalve should be open and the second closed to compress the gas or thatthe second valve should be opened and the first one closed to exhaustthe gas. In another embodiment, the above mentioned patent suggests thata reciprocating piston may be used to compress and expand the gas withinthe system. Although this scheme eliminates the judgment of an operator,the timing of the compression and expansion cycle of the gas is doneindependently of the refrigerating requirements.

Therefore, one object of this invention is to provide means with nomoving parts to control the movement of gas into and out of the pulsetube refrigerator.

Another object of this invention is to use the pulse tube refrigeratorto control the period of oscillation of the gas moving into and out ofthe pulse tube refrigerator.

Briefly, this invention includes a fluid device that has one fluid inletcommunicating with two diverging outlet legs. One of the legs is coupledto the regenerator for the pulse tube refrigerator. At the point ofjunction of the two legs, there is a pressure or vacuum lateral controlarrangement by which the flow of fluid to one or the other leg can becontrolled. The control arrangement senses the pressure in theregenerator. Thus, when a compressable fluid such as air is fed into thefluid device, the air exits through the leg coupled to the regenerator.This causes the pressure within the regenerator and pulse tuberefrigerator to build up. When the pressure builds up to a predeterminedvalue, the control arrangement, since it senses the pressure in theregenerator, switches the flow of air to the other leg. The pressure inthe regenerator and pulse tube refrigerator drops as the air therein isable to exit through the fluid device. When the pressure in theregenerator reaches a predetermined lower limit, the control arrangementhas insufficient pressure applied thereto and the flow of air switchesback to the first leg to again compress the air within the regeneratorand pulse tube refrigerator. The cycle is repeated auto matically. 7

These and other objects, features and advantages will become moreapparent from the following description of a preferred embodiment of theinvention selected for pur- 3,314,244 Patented Apr. 18, 1967 poses ofillustration and shown in the accompanying drawing, in which FIG. 1shows schematically the pulse tube refrigerator and regenerator incombination with a fluid switching device;

FIG. 2 is a graph showing the temperature at various positions along therefrigerator and regenerator when the system is in equilibrium; and

FIG. 3 shows schematically an enlarged sectional view of the fluidswitching device shown in FIG. 1.

Although a pulse tube refrigerator is part of the prior art, first willbe explained the method of operation of the pulse tube refrigeratorsince it is a relatively new art. In general, the method is based uponthe concept of a heat exchange mechanism which operates to provide botha cooling effect in a first part of a confined space and a heatingeffect in a second part of the confined space in such a manner that heatis pumped from the first part to the second part.

Referring to FIG. 1, the pulse tube refrigerator achieves this result byhaving an oscillating pressure exerted on a gas confined within atubular enclosure 10. A pressurized volume of gas is caused to move intoand out of the tubular enclosure 10 by a compressed air supply means 22in a novel manner to be hereinafter described. The pressurized volumeenters the enclosure 10 through a conduit 11 provided at one end thereofand then exits out of the same conduit 11. However, a laminar flowpattern parallel to the axis of the tubular enclosure 10 is maintainedby an element 12 preferably made of a porous metallic material such assintered bronze. The compressed air, entering through conduit 11,disperses within a chamber 13 disposed between the sintered element 12and the base of the enclosure 1%). The compressed air then passesthrough the element 12 compressing the molecules within enclosure 10causing the temperature to rise. At the other end of the enclosure 10 isdisposed a heat exchanger 14 which is cooled by, for example, waterflowing through tubes 16 and 17. The heat exchanger 14 removes heat fromthe compressed air. After the heat is removed the air within theenclosure 10 is allowed to expand by removing the pressure from conduit11. In expanding, the gas within the enclosure is cooled. This cycle isrepeatable and each time heat is absorbed by the gas from the sinteredelement 12 and heat is given up by the gas to the heat exchanger 14. Toproduce refrigeration more efficiently and at much lower temperatures, aregenerator 18 is provided between conduit 11 and the compressed airsupply means 22. After the system reaches equilibrium a temperaturegradient is produced along the regenerator and the pulse tuberefrigerator such as shown in FIG. 2. The compressed pair enters theregenerator 18 through a conduit 19 and the air is cooled as it passesthrough the regenerator as shown by the curve between points A and B onthe graph. The temperature of the gas is constant between the time itleaves the regenerator (point B on the graph) and the time it exitsthrough the sintered element 12 (point C). The temperature of the gaswithin the enclosure 10 follows the curve from points C to D duringcompression. After the gas is compressed, the gas is cooled by the heatexchanger 14 to point B (approximately the temperature of the waterentering and leaving tubes 16 and 17). The gas is allowed to expand andas the gas expands the temperature follows the curve from points E to F.It is noted that the gas approaches the sintered element 12 duringexpansion at a lower temperature than the gas which left the sinteredelement during compression. As the gas passes through the sinteredelement 12 it absorbs heat from a cold plate 21 disposed in heatconducting contact with the sintered element 12, as shown by thetemperature curve from points F to G.

As mentioned previously, the prior art uses moving mechanisms to causecompression and expansion of the gas within enclosure 10. However, themeans 22 in this invention for causing compression and expansion of thegas in enclosure has no moving parts. Referring to FIG. 3, the means 22is shown in cross-section and enlarged. The means 22 is a fluid devicehaving an inlet 23 and two outlet legs 19 and 26 that branch from theinlet to assume a Y shape. The inlet 23 and the leg 19 are preferablydisposed substantially on a straight line to provide the fluid devicewith memory. In the general area of the junction of the two legs 19 and26, there is a side pressure or vacuum control arrangement in the formof a relatively small bore 27. The bore 27 is disposed on the same sideas leg 19 and is coupled to and communicates Withthe regenerator by atube 28. As mentioned before, the leg 19 is also coupled to theregenerator 18.

The fluid device operates as follows: Compressed air is coupled to inlet23. The inlet 23 is so shaped to ensure that air at subsonic velocitiespasses through a throat section 29. Since the fluid device has beenconstructed with memory, i.e., the stream of air has a tendency to passthrough leg 19 into the regenerator 18. The pressure in the regenerator18 increases and, when the pressure rises to predetermined value, thepressure, being fed to the bore 27 by tube 28, causes the stream of airto switch to the other leg 26. This causes the pressure in theregenerator 18 to drop. The air in the regenerator 18 is able to exhaustout of leg 19 and turn around within the fluid device due to reaction ofthe main stream of air therein leaving the throat section 29. The airfrom the regenerator and the main stream of air exit through leg 26. Leg26 is made sufficiently large to conduct both the main stream of air andthe air from the regenerator. When the pressure in the regenerator 18drops to a predetermined level, the pressure at bore 27 is insuflicientto hold the stream of air so that the stream exits through leg 26 andthe stream of air switches back to leg 19. The air in the regenerator isagain compressed and the cycle is repeated.

It is to be noted that the slope, that a section of an interior wall 31to the right of the throat section 29 makes with the axis of the inlet23, determines the maximum pressure that the regenerator would besubjected to before the stream of air is switched to flow out of leg 26.Then, when the stream of air has switched, it tends to stick to aninterior wall 32 and less pressure through bore 27 is required to holdthe stream than to switch the stream. The slope, that the section of thewall 32 to the right of the throat section 29 makes with the axis of theinlet 23, determines what predetermined minimum pressure that theregenerator would be subject to before the pressure therein is caused torise by the means 22 switching.

Thus, the novel combination of the fluid device and the pulse tuberefrigerator enhances the results achieved in the system, because thecompression cycle is continued until the pressure in the system rises tothe predetermined level before the stream of air is switched. Thisensures maximum compression during each cycle. Then, the expansion cyclecontinues until the predetermined minimum pressure is attained. Thus,when more or less refrigeration is required, the timing of therefrigeration cycle adjusts itself automatically to the needs. This isaccomplished without the use of moving mechanism, i.e., having no movingparts. This is a desirable feature because a relatively inexpensivesystem is able to operate reliably at extreme ambient temperatures.

With the present disclosure in view, modification of the invention willappear to those skilled in the art. Accordingly, the invention not to belimited to the exact details of the illustrated preferred embodiment butincludes all such modification and variations coming within :he scope ofthe invention as defined in the appended :laims.

What is claimed is: I

1 In combination, a pulse tube refrigerator comprisa tubular enclosuredisposed to receive gas under pressure at one end thereof,

a flow smoothing heat exchanger disposed at said one end of saidenclosure for smoothing the flow of gas entering said enclosure,

means for removing heat at the other end of said en closure, and

means for cyclically increasing and decreasing the pressure of the gaswithin said enclosure;

said means for cyclically increasing and decreasing the pressure of thegas including conduit means for supplying gas under pressure;

a fluid switching means having an inlet connected to said conduit means,and two outlets communicating with said inlet, and one of said outletscommunicating with said one end of said enclosure; and

fluid control means disposed on said fluid switching means forcontrolling the exit of the gas from the switching means into one or theother outlet.

2. In the combination of claim 1 wherein:

said fluid control means includes at least one bore formed in saidswitching means and communicating with one of said outlets substantiallyadjacent to the junction of said two outlets to cause the gas to bedeflected to said other outlet when pressure is applied to said bore andto allow the gas to deflect back to said one outlet when no pressure isapplied to said bore.

3. In the combination of claim 2 wherein:

said bore communicates with said tubular enclosure to cause the pressurewithin said tubular enclosure to be fed to said bore to deflect the gasto said other outlet when the pressure rises to a predetermined level.

4. In the combination of claim 3 wherein:

said inlet and said one outlet of said switching means are substantiallyaligned to provide memory for said switching means to tend to direct theflow of gas to said one outlet rather than to said other outlet.

5. In the combination of claim 1 wherein:

a regenerator is disposed between said fluid switching means and saidtubular enclosure and said one outlet communicates with said regeneratorwhich in turn communicates with said enclosure.

6. In the combination of claim 5 wherein:

said fluid control means includes at least one bore formed in saidswitching means and communicating with one of said outlets substantiallyadjacent to the junction of said two outlets to cause the gas to bedeflected to said other outlet when pressure is applied to said bore andto allow the gas to deflect back to said one outlet when no pressure isapplied to said bore.

7. In the combination of claim 6 wherein:

said bore communicates with said regenerator to cause the pressurewithin said regenerator to be fed to said bore to deflect the gas tosaid other outlet when the pressure therein rises to a predeterminedlevel.

8. In the combination of claim 7 wherein:

said inlet and said one outlet of said switching means are substantiallyaligned to provide memory for said switching means to tend to direct theflow of gas to said one outlet rather than to said other outlet.

9. In the combination of claim 8 wherein:

said inlet is shaped to cause the gas to pass therethrough at subsonicvelocities.

10. In the combination of claim 8 wherein:

said one outlet has a smaller cross-section than said other outlet.

11. In combination, a pulse tube refrigerator comprismg:

a tubular enclosure disposed to receive gas under pressure at one endthereof,

a flow smoothing heat exchanger disposed at said one end of saidenclosure for smoothing the flow of gas entering said enclosure,

means for removing heat at the other end of said enclosure,

means for cyclically increasing and decreasing the pressure of the gasWithin said enclosure, and

means for sensing the pressure Within said enclcsure pressure should beincreased and decreased in response to the pressure within saidenclosure.

References Qited by the Examiner UNITED STATES PATENTS 1,321,343 11/1919Vllilleurnier 6Z33 1,459,270 6/1923 Vuilleurnier 62-88 3,237,421 3/1966Gifiord 6288 and for controlling said second means as to when the 1WILLIAM J. VVYE, Primary Examiner.

1. IN COMBINATION, A PULSE TUBE REFRIGERATOR COMPRISING: A TUBULARENCLOSURE DISPOSED TO RECEIVE GAS UNDER PRESSURE AT ONE END THEREOF, AFLOW SMOOTHING HEAT EXCHANGER DISPOSED AT SAID ONE END OF SAID ENCLOSUREFOR SMOOTHING THE FLOW OF GAS ENTERING SAID ENCLOSURE, MEANS FORREMOVING HEAT AT THE OTHER END OF SAID ENCLOSURE, AND MEANS FORCYCLICALLY INCREASING AND DECREASING THE PRESSURE OF THE GAS WITHIN SAIDENCLOSURE; SAID MEANS FOR CYCLICALLY INCREASING AND DECREASING THEPRESSURE OF THE GAS INCLUDING CONDUIT MEANS FOR SUPPLYING GAS UNDERPRESSURE; A FLUID SWITCHING MEANS HAVING AN INLET CONNECTED TO SAIDCONDUIT MEANS, AND TWO OUTLETS COMMUNICATING WITH SAID INLET, AND ONE OFSAID OUTLETS COMMUNICATING WITH SAID ONE END OF SAID ENCLOSURE; ANDFLUID CONTROL MEANS DISPOSED ON SAID FLUID SWITCHING MEANS FORCONTROLLING THE EXIT OF THE GAS FROM THE SWITCHING MEANS INTO ONE OR THEOTHER OUTLET.